A hybrid vehicle in which an internal combustion engine, a motor generator, and an output shaft are connected to different rotational elements to each other of a planetary gear unit so as to continuously change a ratio between a speed of the internal combustion engine and a rotational speed of the output shaft, that is, a transmission gear ratio in the planetary gear unit and the motor generator has been known. As a drive system of such a hybrid vehicle, a system that includes two planetary gear units and a brake to realize a continuously variable state in which the transmission gear ratio is continuously changed by these and a overdrive state in which the speed of the internal combustion engine is lower than the rotational speed of the output shaft has been known (see Patent Literature 1). In this system of Patent Literature 1, only one planetary gear unit of the two planetary gear units is used to transmit rotation in the case of the continuously variable state. Thus, mechanical loss is suppressed.